Ultrasound dating birth

In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity.

In contrast, our mean birth weight at 40 weeks (3522 g) is about 120 g higher, at 41 weeks (3652 g) 167 g higher, and at 42 weeks (3750 g) 260 g higher than previous British birthweight standards, which are based on menstrual dates and show considerable flattening at term.2We have since examined our accuracy of gestational dating by ultrasound measurement of the fetal biparietal diameter using Campbell and Newman's dating tables.4 We studied 19 consecutive singleton, normal term pregnancies resulting from assisted conception by in vitro fertilisation or intrauterine insemination booked at our hospital.If you have an irregular cycle, or if you've recently been taking the contraceptive pill, working out the date from your LMP isn't a very accurate method.Ultrasounds are more accurate than using the LMP and, if the ultrasound date differs from your period dates, the ultrasound date will be used.EDITOR, - Tine Brink Henriksen and Allen Wilcox1 comment on our finding that the birthweight curve in our study was steeper at term than that observed in other studies.2 We ascribed this to our use of dates based on routine ultrasound scans instead of menstrual dates to derive our weight for gestational age standard.2 They suggest that a constitutionally large fetu's gestational age is overestimated by the dating scan and that therefore bigger babies, with presumably larger birth weights at term, would selectively be plotted against later gestations, thus creating bias.While it is true that the study they refer to showed variation in biparietal diameter between small (=90th centile) babies,3 the difference between these extremes amounted to only about 1.5 mm at 18 weeks (figure 2 in reference 3).The LMP is used because most women know when their last period was, but may not know when they actually conceived.

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